The present invention relates to novel terpolymers of tetrafluoroethylene and ethylene and a process for producing the same. More particularly, it relates to novel terpolymer of tetrafluoroethylene and ethylene having improved properties which are produced by copolymerizing tetrafluoroethylene and ethylene with a small amount of a specific fluorovinyl ether, and the process for producing the same.
It has been known to produce copolymers of tetrafluoroethylene and ethylene which are characterized by excellent chemical resistance and excellent thermal stability and good electrical properties by copolymerizing tetrafluoroethylene and ethylene in the presence of a polymerization initiator. These copolymers are known to be useful as a raw materials for preparing various shaped articles, electric wire coating and corrosion resistant linings, and coatings, etc., because of their excellent properties, and significant melt processability.
It has been proposed to copolymerize tetrafluoroethylene and ethylene with an auxiliary amount of a vinyl comonomer which has no telogen activity and causes a side chain having at least two carbon atoms in order to improve physical characteristics at high temperature especially tensile characteristics at high temperature for copolymers of tetrafluoroethylene and ethylene (such as Japanese Patent Publication No. 23671/1972, U.S. Pat. No. 3,624,250, and British Pat. No. 1,292,643).
In accordance with these processes, it is possible to overcome the disadvantage that a coating of a copolymer of tetrafluoroethylene and ethylene on a wire becomes brittle at high temperature to cause cracks even under low stress.
However, when the vinyl comonomer which forms a side chain having at least two carbon atoms, is used, the advantageous effect can be attained for improvement of tensile characteristics at high temperature but various disadvantages are found in industrial purposes. For example, when the copolymerization of tetrafluoroethylene and ethylene is carried out by adding a perfluoroolefin having the formula EQU CF.sub.2 .dbd.CF--Rf
such as EQU CF.sub.2 .dbd.CF--C.sub.2 F.sub.5 and CF.sub.2 .dbd.CF--C.sub.4 F.sub.9,
the reaction velocity of the copolymerization is remarkably low. When a hydrofluoroolefin or a vinyl ester comonomer such as EQU CH.sub.2 .dbd.CH--CH.sub.2 --C(CF.sub.3).sub.2 OH or ##STR1## is copolymerized, the resulting copolymer has a lower heat resistance, for example, the heat resistance of longer than 200 hours in an ageing test at 230.degree. C. for measuring the period for which the elongation at 23.degree. C. becomes half compared with initial elongation is decreased to 80 to 100 hours or lower by the introduction of the side chain in the copolymer of tetrafluoroethylene and ethylene.
In U.S. Pat. No. 3,624,250 and British Pat. No. 1,292,643, vinyl monomers having a multiple bond, an acidic group or an ester group in the side chain are not used as the vinyl monomers having a large side chain. For example, vinyl esters, unsaturated carboxylic acids, and alkyl esters of unsaturated carboxylic acid are not used. It is not clearly understood the reason why such vinyl monomers are not used, but it is presumed to be for reason of inferior heat resistance in ageing etc. It is difficult to improve the tensile characteristics at high temperature without copolymerizing them in high degree when vinyl acetate is used. As the result, the inferior heat resistance in ageing and inferior tensile creep property result.